Wilson power and distribution transformers at Cernay-lès-Reims BESS France

Projects
Cernay-lès-Reims BESS

240MW/480MWh France’s Largest BESS

Located in the Marne region of north-eastern France, the Cernay-lès-Reims Battery Energy Storage System (BESS) is the largest battery energy storage site in France at the time of energisation. With a power capacity of 240MW and an energy storage capacity of 480MWh, the project is more than double the size of the country's next-largest operational site. It represents a major milestone in France’s energy transition, significantly strengthening the electricity grid and enhancing its ability to integrate large-scale renewable energy generation. Developed by TagEnergy, the project uses Tesla Megapack battery technology and connects to France's 225kV national transmission network through grid connection partner RTE.

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Sector	Battery Energy Storage System
Developer	Tagenergy
Location	Reims, France
Scope of Work	Two 100/130MVA 225/33kV Wilson Power Transformers Seventy-one 4.2MVA 33kV/480-480V Wilson T2 Ecotrans® Large Distribution Transformers Two 150kVA 33kV/415V Wilson Auxiliary Earthing Transformers

Wilson power & distribution transformers at Cernay-lès-Reims BESS France

Wilson Power Solutions supplied a complete transformer solution under contract with Tesla France SARL, forming the core electrical infrastructure of the site. This included two 100/130MVA 225/33kV Wilson Power Transformers, seventy-one 4.2MVA 33kV/480-480V Wilson T2 Ecotrans® Large Distribution Transformers, and two 150kVA 33kV/415V Wilson Auxiliary Earthing Transformers, totalling 75 units.

Each Wilson Power Transformer is rated at 100/130MVA and steps down from France’s 225kV national transmission grid to 33kV across the site. Both units are fitted with an On-Load Tap Changer (OLTC), providing continuous voltage regulation under live load without de-energising the transformer, which is essential for managing the rapid and variable power flows of a 240MW battery storage platform operating across frequency response, capacity, and balancing services.

140

Tesla megapacks

480 MWh

battery energy storage capacity

60000

home powered

for two hours

The seventy-one Wilson T2 Ecotrans® Large Distribution Transformers are custom-engineered to interface directly with the Tesla Megapack battery units, each featuring a dual 480-480V LV winding. All units are filled with FR3 natural ester fluid, a renewable and biodegradable alternative to mineral oil with a significantly higher flash point that enhances fire safety and reduces environmental impact. The two Wilson Auxiliary Earthing Transformers, also FR3-filled and hermetically sealed, provide earthing protection and supply a balance of the site requirements.

Backed by a €250 million investment, the project will deliver fast-response grid flexibility, enable the secure integration of renewable energy sources, and support supply stability during peak demand periods. With a storage capacity equivalent to approximately 20% of residential electricity demand in the Marne region, the system will serve more than 565,000 residents and play a key role in improving the resilience and flexibility of the French electricity system.

Erika Wilson - Managing Director

Wilson Power Solutions

“Our work with TagEnergy has scaled from Lakeside in the UK to Cernay-lès-Reims, now France’s largest transmission-connected Battery Energy Storage System. These projects reflect how quickly battery storage is evolving in size and complexity, and we’re proud that our transformer technology is helping make that scale possible while strengthening grid resilience and enabling higher levels of renewable energy integration.”

Erika Wilson - Managing Director

Wilson Power Solutions

The project marks another significant milestone in Wilson Power Solutions’ growing involvement in large-scale European energy storage infrastructure. Cernay-lès-Reims reinforces our role in delivering high-performance transformer solutions that support the transition to resilient, low-carbon power networks.